In today's information age, communication systems carry voice, fax, data, video, and other information over a variety of communication media using a variety of communication technologies. In such communication systems, communication signals often become distorted from a variety of causes.
One type of distortion occurs when a transmitted signal is reflected back to a communication device as part of a received signal. Depending on the type of communication channel involved, the received signal can include a single echo or multiple echoes of the transmitted signal. This echo component of the received signal can cause errors and other problems unless the communication device removes, reduces, or otherwise compensates for the echo component.
Therefore, the communication device typically includes an adaptive filter for canceling the echo component of the received signal. For convenience, this adaptive filter is often referred to as an echo canceller.
The echo canceller design depends upon a number of factors, including the echo channel impulse response length of the communication channel. In communication systems having large delays, the echo channel impulse response can be quite long. In such communication systems, an echo canceller that covers the entire echo channel impulse response can be highly complex and require substantial processing resources. Such an echo canceller is typically also slow to converge.